Why should you care?

ShopNest “open orders over 1000” must filter in the database, not load millions into memory.

See it live — copy this example

Paste into a C# console or class library project and run dotnet run.

using System.Linq.Expressions;
public interface IExpressionSpec<T>
{
    Expression<Func<T, bool>> ToExpression();
}
public sealed class OpenHighValueSpec : IExpressionSpec<OrderRow>
{
    public Expression<Func<OrderRow, bool>> ToExpression() =>
        o => o.Status == "Open" && o.Total >= 1000;
}
public sealed record OrderRow(string Status, decimal Total);

var spec = new OpenHighValueSpec().ToExpression().Compile();
Console.WriteLine(spec(new OrderRow("Open", 2500)));
// In EF: db.Orders.Where(new OpenHighValueSpec().ToExpression());

Run Example »

Edit the code below and click Run to see the result in Toolliyo’s live editor.

What happened?

• Expression specs compose into IQueryable.
• In-memory Compile helps unit tests.
• This deepens the earlier boolean specification lesson toward EF.

Practice next

1. Compile and test the sample.
2. Use Where(spec.ToExpression()) in EF.
3. Compose AndAlso expressions carefully.
4. Parameterize min total.
5. Add AsNoTracking query.

Remember

Expressions for SQL. Same rule names as domain. Filter in the database.

ShopNest EF open-order query

Ops list uses OpenHighValueSpec in EF Where.

Outcome: SQL filters; memory stays calm.